Vacuum tube



W. L. KRAHL Aug, 2, 1932.

VACUUM TUBE Filed Oct. 8, 1926 av 094 x 502; WALTER LOUIS KRAHL 1g1t- @Momw why Patented Aug. 2, 1932 UNITED STATES PATENT OFFICE WALTER LOUIS KRA H L, OF HARRISON, NEW JERSEY, ASSIGNDR TO AROD'U'RUS RADIO TUBE COMPANY, OF NEWARK, NEW JERSEY, A CORPORATION OF DELAWARE vacuum TUBE Application filed October 8, 1926. Serial ll'o. 140,245.

This invention relates to electron emitting devices of the general type known as vacuum tubes and more particularly of the type utilizing as a cathode a surface coated or treated with material adapted to emit electrons when heated and provided with a heater 'disposed in such relation to said surface as to maintain it at a temperature such that it emits electrons.

It is an object of this invention to provide a tube of the character described capable of use as an amplifier, detector, rectifier and the like and which may be energized directly from the house lightin circuit without the .15 necessity of using recti ers, battery eliminators and the like.

It is a further object of this invention to provide a tube of the character described which is relatively inexpensive to manufac- 2 ture and which will operate at high efficiency with maximum freedom from hum and other disturbing noises usually characteristic of devices of the same general nature operable from commercial lighting and power circuits, and which will have a long operating life of high reliability.

It is still a further object of this invention to provide a tube of the character described which shall be mechanically as strong and rugged as possible and which will be characterized by high thermal efliciency and minimum operating lag.

It is still a further object of this invention to rovide a tube of the characterdescribed which may be provided with a standard base to be mounted in a standard socket without requiring any changes in the wiring of the socket or the apparatus with which the socket is associated; for example, when it is desired to use the tube in a radio receiver, the tube may be inserted in any standard type of radio receiver without requiring any changes whatsoever in the wiring of said receiver, to convert said receiver to operate from the house lighting circuit.

Further objects of the invention relate to utilization of a series connection and elimination of a solid di-electric between the heater and the cathode, the reduction of the tube base My invention itself, however, both as to its underlying princi les and as to its practical embodiments will est be understood by reference to the specification and accompanying drawing, in which Figure 1 is a diagrammatic view of a tube according to my invention,

Figure 2 is a perspective view of a detail thereof, and Fig. 3 is a sectional side elevation showing the manner for mounting the side terminal.

In accordance with my invention, I provide a cathode comprising a cylindrical sleeve of conducting material such as nickel, coated on the outside or treated with substances adapted to emit electrons when heated, such as oxides of barium and strontium. I arrange a heater within this sleeve in such manner that the heat developed by the heater when an electric current is passed therethrough is transmitted to the cathode by radiation and maintains it at such a temperature that a streamof electrons is emitted.

In order to provide a tube as strong and rugged as possible and at the same time as economical as possible, the electrodes are all 4 supported from a single stem orpress and the supporting members extending into said press form the sole support and the sole contacting leads to'the electrodes.

In order to eliminate the necessity for using an insulating shield between the heater and the cathode, I arrange the cathode with its longitudinal axis parallel to the lead-in wires and arrange a direct metallic connection between the outer end of the heater and the cathode, The inner end of the heater is supported in spaced relation with respect to the cathode by a relatively short andstiff lead-in wire embedded in the press, and the lower end of the cathode is similarly supported, thereby positively maintaining said heater out of contact with said cathode at the lower end and eliminating the necessity for an insulating shield interposed between the heater and cathode. By this construction the heater and cathode are spaced apart and yet are electrically connected.

The tubular cathode extends to the press or support so that the heater is shielded from a point adjacent the low potential junction point of cathode and heater throughout its length to the press. This construction is deemed to accomplish an important result a will be pointed out hereinafter.

To obtain a filament of long life and extreme reliability I prefer to make use of a carbon filament which performs the function of heater, and in order to support said filament in a manner to compensate for variations of temperature, the outer end is resiliently supported, and as a support, I prefer to use a spring of tungsten or other suitable material. It is evident that carbon cannot be welded to tungsten and for the purpose of making a welded joint possible, I prefer to coat the end of the carbon filament with a material capable of being welded to the hook. This may be done by first electroplating upon the end of the filament a deposit of copper and then electroplating upon the copper a coating of nickel. The copper adheres to the carbon, the nickel adheres to the copper and the nickel may be welded to tungsten. A similar arrangement may be utilized at the lower end of the filament, but in case the lead-in wires are of nickel, it will not be necessary to make a separate plate of nickel upon the copper as the nickel and copper may be welded directly.

The tube is arranged to be provided with a standard base comprising a pair of filament terminals or contact prongs adapted to make contact with appropriate contacts in a standard socket. In order to permit of the use of alternating current derived from the house lighting system without making changes in the wiring of the usual radio receiver necessary, I prefer to connect the two filament prongs of the base together and to connect these prongs to one end of the heater, the other end of which is connected to a terminal carried b the tube in some way which will not inter ere with the insertion of the tube in a standard socket; for example, this terminal may be in the form of a spring clip carried on the side of the tube and above the base, whereby one terminal of the power lead may be connected to the A-plus or A-minus terminal of the receiver in order to obtain the benefit of a variable rheostat which may be connected in the filament circuit, and the other terminal will-be connected to the clip mentioned.

Referring now to Figure 1,-1 designates suitable metallic material coated with a substance adapted to emit electrons when heated. Preferably for the sleeve I employ a magnetic metal, such as nickel in the form of a cylindrical shell, the diameter of which is small compared with the length. For the coating various mixtures of the general type referred to are known and it is ,clear that any suitable mixture may be used. I have found, however,

that excellent results may be obtainedwhen barium coating'is applied in a single application and the wax burned off after which the cylinders are placed in an oven in an atmosphere of hydrogen and baked at red heat until the oxides are transparent, after which the cylinders are allowed to cool and are ready to be mounted in the tube assembly.

4 is the heater comprising, as already stated, a carbon filament. 5 is a stem or press through which the lead-in wires pass formed in the flare tube 6. 7 is the envelope sealed to the flare tube 6. The envelope may be of clear glass or may have a metallic deposition on the inner or outer surface thereof. The envelope with the elements enclosed is mounted in base 8 provided with contact pins 9, 10, 11 and 12, and a suitable spring clip 13 is held in position by means of a rivet 15a and by a fibre extension 14 passing Within the base 8 between the cathode terminals 10 and 11. The

connector 65 between these electrodes passes over and holds the extension 14 in place. 16 designates the coating' on the lower end of filament 4, and 17 the support wire connected to lead-in wire welded thereto. 18 designates a similar coating on the upper end of heater or filament 4, and 19 a spring preferably of tungsten welded to the filament on one end and having the other end welded to filament supporting wire 20; wire 20 is embedded at its lower end in press 5.

The cathode may be provided with a collar 22 at its lower end which may be welded to a suitable support wire 22a also embedded in I press 5 and contacting with lead-in wire 22b, and connected likewise to pins 10 and 11. A suitable collar 23 may be formed on the top of the cathode and welded to support 20 by connection 50, which, it will be seen, provides a direct and positive metallic contact between the cathode 3 and the top of the filament or heater 4. The grid or control electrode 2 is preferably formed of'a coil of wire with wound upon grid supports 24 and 25 embedded in the press and making contact grid lead 26. In a similar manner the plate is supported by wires 27 and 28 embedded in the press 5, and to provide additional rigidity, the plate support 27 may be extended in the element 51 which is bent outward and downward and embedded in less head 30 formed on support 20. The gri element 68 is also supported by rod 69 in the bead 30. Plate support 27 makes contact with plate lead 29 passing through the press to the appropriate prong 12 of base 8. The lower end of the filament to which the coating 16 is a plied is connected to supporting wire 17 embedded in the press which in turn is connected with lead-in wire 17 a passing through the press and making contact with terminal 15.

' A suitable transformer 31 comprising primary and secondary windings may be provided for stepping down the voltage derived from the house lighting system designated as 32. It will now be seen that if one of the secondary leads from transformer 31 is connected to terminal 15, which may be done without in any way disturbing the connections of the receiving apparatus, the other terminal of the secondary winding of transformer 31 may be connected to either the A plus orA-minus terminal of the receiver, in which case the heater'will be energized, and the current flowing therein may be controlled by the rheos'tat usually found in the receiver provided the connection has been made to the A terminal which includes the rheostat in circuit.

. Since ,no insulating sleeve is provided between the heater or filament 4 and the cathode 3, the cathode will very quickly reach temperature equilibrium and the tube will therefore quickly reach normal operating condition when the filament is energized.

It is also to be noted that since the top end of the filament or heater 4 is directly connected to cathode 3, no harm can result in case the top end of filament 4 comes directly in contact with the nickel sleeve forming the oathode 3. Since, however, the lower end of the filament 4 is at a different potential from cathode 3, this end must not be permitted to come in contact with the cathode, but by reason of the proximity of the lower end of the electrodes to the press, these ends are rigidly supported against movement, whereby it will be seen that by this construction I am enabled to avoid the use of an insulating shield between the filament4 and the cathode 3 and at the sametime provide a cathode very closely encircling the heater, whereby a high thermal efficiency is realized, and time lag in operation minimized.

The coating, as prepared in the above or similar manner, is applied to a length of the sleeve such as is included between the ends of the enclosing cylindrical plate, so that a minimum amount of electronic dlscharge occurs lKi tthe tube interior and envelope beyond the p a e.

Due to various electrical conditions within and without the tube, giving rise to a relatively high potential on the envelope, it has been found desirable in some instances to ground the envelope surfaces 66 and 67, or otherwise make connection to a point of low otential. This may be accomplished either y metallic deposition on the lass interior or exterior, formin a film, or by the use of metallic strip app ied to the bulb, and in either instance, a ground connection made as at 70 to the outside surfacing.

The structure of the units with the relatively high resistance carbon heater rod'4 and the cathode 3 in series is advantageous, moreover, as it reduces the current and hence the induction effective in the production of hum. The filament life is also increased. Also the parallel relationship of the heater and cathode cylinder tends to diminish the inductive effects due to variable current flow through these elements. In addition the nickel shell acts as a shield serving to neutralize the electrostatic action of the heater circuit and hence it complements the other factors mentioned-in reducing hum arising from the low frequency power current.

While the outstanding object of the inventionto reduce alternating current humis facilitated by the above mentioned factors, stress should be laid on the use of the completely shielded heater filament and the elimination of the ion active material from the exposed portions of the cathode. Since the potential of cathode and filament adjacent their junction 52 is practically equal, no shielding is there necessary but the difference in potential between the exposed vertical length of the filament and base connection 16 on the one hand and adjacent cathode on the other hand, is appreciable, and applicant has discovered that complete shielding of these parts is essential to obviate hum to the greatest possible degree.

Also, the active material coating the oathode, if unshielded, has been found to transmit variable electrical impulses to the tube interior and cause hum. The limitation of the coating within the space defined by the enclosing cylindrical plate practically eliminates this disturbance. Note should be made further of the utility of the series connection which permits'elimination of one base terminal and lead wire of the tube. 4

It is clear that the construction described is useful not only in amplifiers and detectors, but is also capable of use as a rectifier, in which case it is unnecessary to provide the grid. It is also clear that another terminalment to a metallic spring not capable of being filament so that heating current may be supplied to the filament without passmg through the wiring of the receiver. Also, while carbon is specified for the heater, may use other high resistance material whlch may be wholly metallic in composition.

While I have shown and described a preferred embodiment of my invention, it is 5. In a vacuum tube, an anode; a cathode comprising a surface adapted to be heated to emit electrons; a heater arranged for heating said cathode; a single press; a standard base having a pair of contacts extending therefrom arranged to make contact with the filament terminals of a standard socket, said contacts being connected together and to one end clear that modifications and changes may be. of said heater; and a connection to the other made within the scope of my invention as will be understood by those skilled in the art.

It is also clear that while I have described my invention as particularly useful for operation on alternating current, it may be used also on direct current, supplied by generators, or by batteries.

I claim:

1. In a vacuum tube, a carbon filament; a metallic spring for resiliently supporting one end of said filament to compensate for variations in length thereof due to temperature variations; a layer of metal which will deposit on carbon by plating formed on said filament; and a second layer of difi'erent metal which will weld to the metallic spring being formed on said first layer, said second layer being welded to said spring, thereby uniting a carbon filament to a metallic spring not capable of being welded to a metal which will plate directly on the carbon.

2. In a vacuum tube, a carbon filament and t a metallic spring for resiliently supporting one end of said filament to compensate for variations in the length thereof with temperature changes; and means for maintaining a metallic connection between said filamentand said spring comprising an adherent layer of metal which will deposit on carbon by plating upon said filament; and a second layer upon said first layer which will adhere to the first layer and can be welded to the spring, said second layer being welded to said spring, thereby uniting a carbon filawelded to a metal which will plate directly on the carbon.

3. The method of establishing a welded metallic connection between-a carbon filament and a metal support therefor'which comprises depositing a layer of adherent metal upon said filament, said coating having greater adherent qualities for carbon than welding qualities for the metal support; depositing a second layer of adherent metal weldable to said support upon said first layer; and welding said second layer to said suport.

4. The method of establishing a welded connection between a carbon filament and a metal support therefor which comprises electro-platingupon said filament acoating of metal adherent to said filament; electro-plating upon said coating a second'coating of metal weldable to said support; and welding said coating to said support.

end of said heater passing through said press and terminating in a contact carried by said base and projecting thereabove in such position as to be accessible when said tube is inserted in a standard socket.

6. In a vacuum tube, an envelope, a cathode within said envelope, a heater adjacent said cathode, a base on said envelope, a pair of terminals on said base extending downwardly therefrom and adapted to make contact with the terminals in a standard socket, a connection between said terminals, a connection from one end of said heater to one of said terminals, an additional terminal mounted on said base and having wire attaching means projecting above the base adjacent the side of said envelope, and a connection between said additional terminal and the other end of said heater.

In testimony whereof I aflix my si ature.

WALTER L. KR L. '95 

